1. Field of the Invention
The present invention relates to a heat generator comprising a working chamber defined in a housing, a viscous fluid accommodated in the working chamber, and a rotor rotationally driven by an external power source. More in particular, the invention relates to a heat generator in which the working chamber includes a heat generating area for accommodating the rotor in such a manner as to secure a fluid-tight gap between the partitioning wall thereof and the rotor for generating the heat by shearing the viscous fluid, existing in the fluid-tight gap, with the rotor, a storage area for accommodating viscous fluid beyond the volume of the fluid-tight gap, and at least one opening in the boundary between the heat generating area and the storage area for communicating between the two areas.
2. Description of the Related Art
A heat generator comprising a viscous fluid (hereinafter referred to as the oil) such as silicone oil sealed in a fluid-tight heat generating chamber defined in a housing in which heat is generated by fluid friction as the oil is sheared by a rotor is known as an auxiliary heat source of an automotive heating system (see, for example, Japanese Unexamined Patent Publication No. 2-246823). In this type of heat generator, the oil constantly subjected to shearing degenerates quickly and the heat generating performance cannot be maintained for a long time. For this reason, a heat generator mechanically designed to prevent or delay oil degeneration as much as possible has been proposed.
An example is a viscous heater (heat generator), disclosed in Japanese Unexamined Patent Publication No. 10-95224, comprising a heat generating chamber and a storage chamber in the housing. The partitioning wall between the heat generating chamber and the storage chamber is formed with at least a recovery hole (recovery path) and at least a supply hole (supply path), through which the viscous fluid is replaced and circulated between the heat generating chamber and the storage chamber. The replacement/circulation avoids the case in which specific oil molecules are subjected to protracted continuous shearing, and allows the viscous oil to rest in the storage chamber to recover its original viscoelasticity. Thus, oil degeneration is delayed. Further, the heat generator described in the same patent publication comprises at least a recovery groove and at least a supply groove extending substantially along the diameter in the inner wall surface of the heat generating chamber in an opposed relation to the shearing surface of the rotor. The recovery groove is for leading the oil from the outer peripheral area of the rotor to the recovery hole, and the supply hole is for leading the oil from the supply hole to the outer peripheral area of the rotor. The recovery groove and the supply groove promote the oil outflow from the heat generating chamber and the oil inflow from the storage chamber to the heat generating chamber to thereby improve the efficiency of the replacement/circulation.
As described above, some patent publications already disclose an idea of an oil shearing type of heat generator comprising a recovery groove (and a recovery path) and a supply groove (and a supply path) formed in the partitioning wall between a heat generating chamber and a storage chamber to promote the replacement/circulation of the oil. Nevertheless, the conditions for arranging the grooves and paths for securing the required heat generating ability while replacing and circulating the oil have yet to be theoretically analyzed or studied in depth. It has thus far been very difficult, therefore, to reflect the idea in the actual machine and commercialize it. Even if the desirable conditions of arrangement have been discovered in the stage of developing a working model of the product, it has been the incidental result of trial and error.